The present invention relates to processes for the preparation of aqueous dispersions of (co)polymerizates using a polymer with cationic functionality and optionally using conventional additives. The invention also relates to the aqueous dispersions preparable with the processes according to the invention, dispersible powders obtainable from the dispersions, as well as the use thereof.
The stabilization of aqueous polymer dispersions (latices) is known from the prior art. Unlike polymer solutions, aqueous polymer dispersions are not thermodynamically stable systems. For this reason to the dispersions are generally added dispersing agents, which have an interfacial stabilizing action. In general, they are water-soluble compounds, present either in the form of protective colloids or emulsifiers. Due to their amphiphilic structure emulsifiers, which usually have a molecular weight below 1500, have a stabilizing action by reducing the interfacial tension between the polymerizate and the aqueous dispersing medium. The stabilizing action of protective colloids is mainly based on a steric shielding of the dispersed particles. They are generally substances with a molecular weight above 1500 and they can be both chemically and physically bound to the dispersed particles. In the widest sense, said protective colloids are themselves polymeric materials, which can therefore impair the action of the modifying polymerizate.
Such stabilizers, which can also be used in emulsion polymerization, are e.g. conventional surfactants, water-soluble polymers, such as polyvinyl alcohol or polyvinyl pyrrolidone, as well as polymerizable monomers. Such polymerizable, functional monomers, which can be used in polymerized form as a substitute for conventional surfactants, are e.g. carboxyl monomers, acrylamides or polymerizable surfactants with sulphonate groups.
A problem when using stabilizing agents is the coalescence, i.e. the undesired flowing together of the latex particles in the emulsion, so that it is no longer possible to obtain a redispersible powder. This agglomeration to larger polymerizate secondary particles (coagulate), for a given polymerizate content of the aqueous dispersion, becomes all the more critical the more finely divided the particles in the disperse distribution, because the interface grows superproportionally with decreasing particle diameter.
Apart from stabilized, aqueous polymerizate dispersions, great significance is in particular attacked to powders rendered available by drying from these dispersions. Redispersible powders are advantageous due to their easy handling, the easier, space-saving transportation, the easier dosability and the less expensive storage. As a result of the readily available dispersing medium (water) the powder form is also desirable in this respect.
The polymer powders produced by drying processes, such as e.g. freeze or spray drying, where in particular in the case of spray drying larger powder quantities can be produced, should be completely reversibly dispersible. However, when adding water, generally not completely satisfactory results are obtained. This is due to the fact that on drying, the highly disperse particles in the dispersion necessarily approach one another until in the case of contact of the surfaces of the particles irreversible changes occur, such as the aforementioned coalescence or also an aggregation of the particles. As a result the surface characteristics of the disperse phase are modified in such a way that on adding water, the affinity of the particles for one another is greater than that to water, so that there is no real redispersion.
In addition, the aforementioned emulsifiers or protective colloids, such as e.g. polyvinyl alcohol, can lead to a reduction of the reactivity of the redispersed polymer particles. In other words, the redispersible powder, following dispersion again, can partly or entirely lose its reactivity, together with the characteristics associated therewith.
One possibility of preventing an irreversible change to the external form of the aqueous polymer dispersion after drying consists of the addition of so-called drying aids, which are also known as spraying aids. These drying aids are water-soluble substances, which on drying form a matrix and in this way embed the polymer particles. On redispersing with water the matrix dissolves again and the polymer particles are reobtained in a virtually unchanged form. EP 770 640 A2 makes use of such a procedure. It describes the preparation of polymerizate powders by drying aqueous polymerizate dispersions, the dispersed polymerizates, which have a positive or negative surface charge, being maintained in solution, accompanied by the addition of a drying aid. This drying aid is a polyelectrolyte, which dissociates into a polyion and a counterion, in which the counterion must have the opposite charge to the polymerizate surface charge. Therefore the polyelectrolyte fulfils the function of an additional stabilizer, which keeps the polymerizate in solution. The polymerizate is not polymerized in the presence of the stabilizer, but is instead present as a finished polymer. The stabilizing effect is here achieved by a further molecule virtually acting as an emulsifier.
Another possibility for obtaining stabilized dispersions from a water-insoluble latex is known from EP 441 037 A1. The latter describes anionically stabilized dispersions from latex and a quaternary, cationic polymer, both components being separately preparable and storable as soluble polymers. Both components are then sprayed together onto the application surface, in order to form a dry coating which cannot be washed out, the cationic polymer serving as a coagulant. Therefore the cationic polymers do not contribute to the stabilization of the dispersion and instead destroy the same, accompanied by the precipitation of the latex polymers (so-called demulsification) and formation of a coating.
EP 286 008 B1 describes the use of aqueous, cationic plastic dispersions for impregnating and priming absorbent substrates. The cationic dispersion polymerizates contain 80 to 99 wt. % ethylenically unsaturated monomers from the group vinyl esters, methacrylic esters, acrylic esters, vinyl aromatics, vinyl chloride, ethylene, acrylonitrile, diesters of maleic acid and/or fumaric acid and vinyl pyrrolidone, 1 to 20 wt. % ethylenically unsaturated, cationic, water-soluble monomers, 0 to 19 wt. % ethylenically unsaturated, hydrophilic monomers with one or more functional groups from the series COOH, xe2x80x94NR1R2, xe2x80x94CONR1R2, in which R1 and R2 stand for H or xe2x80x94CH2OR with Rxe2x95x90H or (C1-C8)-alkyl, and up to 19 wt. % ethylenically unsaturated monomers with one or more OH groups. The monomers are chosen in such a way that the minimum cationic activity of the dispersions is 20 to 200 xcexcmole/g solids, 15- measured at pH 7 and 60 to 99% of the cationic charge is on the surface of the particles, and the dispersions have a minimum film formation temperature (MFT) between 0 and 40xc2x0 C. The polymerizate particles of the dispersions have an average particle diameter of 0.02 to 0.2 xcexcm. The cationic dispersions are used for impregnating and priming brickwork, concrete, plaster surfaces, ground plaster, gypsum surfaces or bricks. However, dispersible powders are not described.
According to JP 55-104 955 A, an aqueous dispersion of a cationic-ethylenically unsaturated polymer is described, which has a glass transition temperature Tg less than 50xc2x0 C. and contains a cationic, water-soluble or water-dispersible, ethylenically unsaturated oligomer and/or polymer and/or cationizable, ethylenically unsaturated monomers in aqueous phase. The polymers serve as additives for improving the characteristics of cement products. As a result there is an improvement to the water resistance, water tightness, strength, adhesion, chemical stability and durability of a cement product, such as mortar. The emulsion polymerization of these polymers is either brought about by radical polymerization of alpha or beta-ethylenically unsaturated monomers in the presence of cationic, water-soluble and/or water-dispersible oligomers and/or polymers or by radical polymerization of alpha or beta-ethylenically unsaturated monomers, which are in part replaced by cationic, ethylenically unsaturated monomers, such as dimethylaminoethyl methacrylate esters of maleic acid, fumaric acid, itaconic acid, etc. This teaching is disadvantageous in that the polymers which can be used are very restricted and there is also a very restricted field of use for the cement formulations. In addition, the polymers produced must have a glass transition temperature Tg less than 50xc2x0 C., in order to e.g. give mortars the desired characteristics.
In addition, the cationic acrylic resin according to this Japanese patent serves as a water dispersing agent and is used as an additional additive. The use of the cationic, water-soluble or water-dispersible oligomer and/or polymer is used for preventing coagulation of the latex in the cement. Moreover, JP 55 104 955 A does not describe a redispersible powder and the latter is also not provided. It is therefore much more difficult to provide, in addition to a stable dispersion, a redispersible powder obtainable therefrom.
The problem of the invention is to so further develop the aqueous dispersions prepared according to the aforementioned processes the whilst maintaining advantageous characteristics or in individual cases for producing improved characteristics, the performance of the process and the choice of the starting materials can be made more flexible. Independently of the functionality of the polymers to be dispersed, the process must also reliably stabilize them in aqueous dispersion. The said dispersions must also be improved so that in their final applications, such as e.g. in plastic-containing, cement-bound systems, they lead to improved use products due to desired consecutive reactions. It must also be possible to obtain from the dispersions a redispersible powder, which substantially maintains its advantageous characteristics, following redispersion in the aqueous medium. It must be possible to obviate the use of stabilizing additives in the form of emulsifiers and protective colloids, as well as drying or spraying aids.
According to the invention, the aforementioned problem is solved by a process A) for the preparation of aqueous dispersions of (co)polymerizates using a polymer with cationic functionality, optionally accompanied by the use of conventional additives, the polymer with cationic functionality being obtained by (co)polymerization in an aqueous medium of olefinically unsaturated (co)monomers, in which at least one (co)monomer has a cationic functionality, further (co)monomers are added and polymerization takes place in the presence of suitable initiators, wherein the polymers and/or (co)monomers are so chosen and the process is so controlled that a (co)polymerizate particle with heterogeneous morphology is formed and the dispersed (co)polymerizate obtained has a glass transition temperature Tg of more than about 50xc2x0 C.
Surprisingly, the polymers with cationic functionality have an action corresponding to an emulsifier or protective colloid for the (co)polymerizate formed according to the invention and during emulsion polymerization lead to a stabilization of the dispersed, copolymerized particles. Through a type of xe2x80x9cpolymerizing inxe2x80x9d of the polymer with cationic functionality, a dispersion-stable latex particle is produced, the latex particles prepared according to process A) having a heterogeneous morphology. In this context, xe2x80x9cheterogeneous morphologyxe2x80x9d need not mean that necessarily two or more different glass transition temperatures Tg must be present. In fact, it means that in the (co)polymerizate particles areas with different compositions, i.e. for example phases, are formed. According to the invention, e.g. an inverse core-shell morphology can be formed. The (co)polymerizate particle can essentially have an outer phase (shell) in the form of substantially hydrophobic areas and an inner phase (core) in the form of substantially hydrophilic areas. Alternatively, with the inventive process, a so-called raspberry-like structure can be produced. Obviously mixed forms with heterogenous morphology are obtainable. Preferably, the emulsion polymerization is performed in such a way that the proportion of polymer with cationic functionality is greater in the outer phase than in the inner phase. The parameters and conditions variable in this connection are known to the expert and reference is made in this respect to xe2x80x9cemulsion polymerization and emulsion polymersxe2x80x9d, P. A. Lovell and M. S. El-Aasser, 1997, particularly pp 293-326.
In the case of the core-shell morphology obtained according to the invention, once again the glass transition temperature can be very important. The glass transition temperature can either be determined by measurement, e.g. using DSC methods, or by theoretical calculation. Within the scope of the present invention, the glass transition temperatures (midpoint temperature according to ASTM D3418-82) of copolymers are calculated by a trial and error method according to Fox (T. G. Fox, Bull. Am. Phy. Soc. (ser II) 1,123 (1956) and Ullmann""s Enzyklopxc3xa4die der Technischen Chemie, vol. 19, 4th edition, Verlag Chemie, Weinheim, 1980, pp 17/18). Thus, for the glass transition temperature is obtained:       1    Tg    =                    w        A                    Tg        A              +                  w        B                    Tg        B              +          …      ⁢              xe2x80x83            ⁢                        w          n                          Tg          n                    
in which
WA+WB+WC . . . =1
and WA, WB . . . represent the mass fractions of the monomers a, b . . . and TgA, TgB . . . the glass transition temperatures of the corresponding copolymers. The glass transition temperatures of certain homopolymerizates of the aforementioned monomers are known and are e.g. listed in Ullman""s Encyclopedia of Industrial Chemistry, VCH, Weinheim, vol. A21 (1992), p 169.
The polymers and/or (co)monomers are chosen in such a way that the dispersed (co)polymerizate obtained has a glass transition temperature Tg of more than about 50xc2x0 C. As is known, the glass transition temperature can be controlled by the choice and quantity of the monomers used. The expert is aware of the criteria for adjusting the glass transition temperature to be applied within the scope of the process according to the invention, so that there is no need for further explanations here. The glass transition temperature Tg of the inner phase (core) and the outer phase (shell) can in each case be modified, in order to permit adaptation to the desired use. If a very rapid film formation is desired, then preferably the inner phase has a very low Tg value, preferably below 50xc2x0 C., so that there is a coalescence of the latex particle. This is advantageous if a continuous dispersion film is to be prepared, which is e.g. the case with coating applications.
If no rapid film formation is to take place at ambient temperature, the glass transition temperature Tg is above 50xc2x0 C. This can be important in corresponding applications, because as a result the stability of the redispersible powders is increased and higher mechanical characteristics of the final application can be obtained.
According to a preferred embodiment, the Tg value of the outer phase is as high as possible and simultaneously the Tg value of the inner phase is as low as possible. It is particularly advantageous if the outer phase has a glass transition temperature Tg of more than about 50xc2x0 C. and the inner phase a temperature of less than about 50xc2x0 C., particularly between about xe2x88x9270 and +50xc2x0 C. This leads to particularly favourable characteristics, because the outer phase gives the sprayed powder an increased stability and the inner phase films the product after redispersion.
The expression xe2x80x9cpolymer with cationic functionalityxe2x80x9d is not particularly restricted, provided that it is obtained by (co)polymerization in aqueous medium of olefinically unsaturated (co)monomers and at least one cationic function is present in the molecule. The term xe2x80x9cpolymerxe2x80x9d covers homopolymers, copolymers, block polymers, graft copolymers, as well as oligomers. It is obvious to the expert that any (co)polymerizable starting monomers with olefinically unsaturated functionalities can be used for this polymer. Preferably, in the polymer with catabolic functionality, for about one part by weight monomer with cationic functionality there are 0 to about 50 parts by weight, particularly about 0.1 to 20 parts by weight of (co)monomer.
The polymer results from co polymerizable, olefinically unsaturated compounds, which are e.g. a vinyl ester of (C1-C18) carboxylic acids, e.g. vinyl acetate, vinyl propionate, etc.; a (meth)acrylate of (C1-C8) alcohols, e.g. methyl methacrylate, butyl methacrylate, octyl methacrylate, ethyl acrylate, isobutyl acrylate, 2-ethyl hexyl acrylate; a vinyl aromatic, such as e.g. styrene, vinyl toluene, vinyl chloride, an ethylene, an acrylonitrile, a diester of maleic acid and/or fumaric acid, a vinyl pyrrolidone, an amino acrylate or methacrylate ester, a vinyl pyridine, an alkylamino group-containing vinyl ether, an alkylamino group-containing acrylamide/methacrylamide or a quaternary ammonium group-containing monomer, such as 2-hydroxy-3-acrylopropyl dimethyl ammonium chloride or 3-methacryloxypropyl dimethyl ammonium chloride or the like. Preferably the cationic functionality is attributed to a quaternary ammonium group. Preferably acrylates and/or methacrylates, as well as ester and amide compounds are used. The chain length between ester/amide and the quaternary nitrogen is typically C2 to C4. It is also possible to use amines protonated in the acid pH-range. According to the invention, particularly preferred monomers for the preparation of the polymer with cationic functionality are e.g.: N,N-[(3-chloro-2-hydroxypropyl)-3-dimethyl ammonium propyl]-methacrylamide chloride (DMA-PMA-epi), N-[3-(dimethylamino)-propyl]-methacrylamide hydrochloride (DMAPMA-HCl), N-[3-(trimethylammonium)-propyl]-methacrylamide chloride (MAPTAC), 2-hydroxy-3-methacryloxypropyl-triethyl ammonium chloride, dimethyl diallyl ammonium chloride, aziridinyl ethyl methacrylate, morpholinoethyl methacrylate, trimethyl ammonium ethyl-methacrylate chloride, dimethylaminopropyl methacrylate, 1,2,2,6,6-pentamethylpiperidinyl methacrylate, aminopropyl vinyl ether, diethylaminopropyl ether and tert-butylaminoethyl methacrylate.
According to the invention, the polymer with cationic functionality can either be prepared in a preceding stage by homo or (co)polymerization of monomers with cationic functionality or with further comonomers and immediately, without being isolated, further processed (in situ further processing). Alternatively the polymer with cationic functionality can firstly be separately prepared and then isolated prior to further processing according to the invention. It is obviously possible to use any commercially obtainable polymer with cationic functionality, which fulfils the aforementioned conditions.
Preferably, in the (co)polymerizate obtained, for about one part by weight monomer (with cationic functionality) of the polymer with cationic functionality, there are about 2 to 250 and in particular about 10 to 150 parts by weight of remaining (co)monomers. According to the invention, the (co)polymerizate prepared contains about 0.001 to 50 mole %, particularly about 0.1 to 35 mole % of monomer units with cationic functionality.
There are no particular restrictions in the present invention with regards to the choice of the (co)monomers, which are polymerized in the presence of the cationic polymer. It is possible to use all (co)polymerizable monomers known to the expert. Reference is made in exemplified manner to alpha, beta-ethylenically unsaturated monomers, such as acrylate esters, methacrylate esters and carboxylate esters, acids and their salts, such as acrylic acid, maleic acid, itaconic acid, vinyl sulphonic acid, vinyl toluene sulphonic acid and unsaturated, dibasic acids, their semi-esters and salts, alpha, beta-unsaturated amides, vinyl esters, vinyl-substituted, aromatic compounds, heterocyclic compounds with vinyl groups, vinylidene halides, alpha-olefins, diallyl phthalates, divinyl benzenes, alkyl acrylates, trimethylol propane trimethyl acrylates, esters of acrylic and methacrylic acid with methanol, ethanol, propanol, butanol, styrenes, alcohols, polyols, glycidyl alcohols, glycols and polycarboxylic acids.
Preferably, apart from cationic monomers, also monomers can be copolymerized, whose protonated, reactive group or groups are deprotonated, accompanied by a corresponding rise in the pH-value. Such groups are known to the experts. Apart from a cationic functionality, there can be at least one anionic functionality in the (co)monomers. Thus, amphoteric systems are obtained, which are stable as such and do not coagulate. These surprising characteristics are not known in this form in the prior art.
The process A) according to the invention can be performed continuously, semicontinuously or as a batch process. This is dependent on whether the polymer with cationic functionality is prepared separately or is further processed immediately following in situ preparation. For example, following the preparation of the cationic polymer, the process can be performed batchwise. In addition, it is clear to the expert that for performing inventive process A), due attention must be paid to the basic rules of emulsion polymerization. Thus, e.g. radical initiators are used for performing the polymerization. There is no relevant restriction to the invention in the choice of initiators. The radical initiators to be used in the invention are either water-soluble or water-insoluble, i.e. they are then monomer-soluble. Suitable water-soluble initiators are sodium, potassium and ammonium peroxodisulphate, hydrogen peroxide and water-soluble azo compounds such as 2,2xe2x80x2-azobis(2-amidino-propane dihydrochloride), 2,2xe2x80x2-azobis[2-methyl-N-(2-hydroxyethyl)-propion-amide] and 2,2xe2x80x2-azobis[2-(2-imadazolin-2-yl)-propane]-dihydrochloride. Suitable monomer-soluble initiators are organic hydroperoxides, such as tert-butyl hydroperoxide, pinane hydroperoxide, p-menthane hydroperoxide, cumene hydroperoxide and diisopropyl phenyl hydroperoxide, organic peroxides, such as dibenzoyl peroxide, dilauryl peroxide and diacetyl peroxide, as well as monomer-soluble azo compounds, such as azoisobutyronitrile. It is also possible to use mixtures of initiators.
In place of a radical initiator it is also possible to use an initiator system, which comprises a radical initiator of the aforementioned type and a water-soluble reducing agent. Thus, the actual radical initiator is formed during polymerization, which is e.g. possible by thermal decomposition of the aforementioned initiator, as well as by the reaction of the initiator with an aqueous reducing agent. The water-soluble reducing agents act as activators for the initiators. Suitable reducing agents are ascorbic acid, sodium, potassium and ammonium sulphite, bisulphite and metabisulphite, sodium formaldehyde sulphoxylate, tartaric acid, citric acid and glucose. They can be used in combination with a heavy metal salt. The reducing agents are generally used in a quantity of 0.01 to 2 wt. %, based on the total monomers added and are usually dosed in during polymerization. The initiators or initiator combination are generally used in a quantity of 0.01 to 2 wt. %, based on the total monomers. Particular preference is given to 2,2xe2x80x2-azobis(2-amidinopropane)-dihydrochloride, hydrogen peroxide and tert-butyl hydroperoxide combined with a reducing agent, e.g. sodium formaldehyde sulphoxylate.
As a function of the use conditions, it is concomitantly possible to use conventional additives. Examples are thickening agents, pigments, flame-proofing substances, crosslinkers, fillers, reinforcing agents, film formation aids, antioxidants, fungicides, foam inhibitors, plasticizers, preservatives, wetting agents, rheology modifying aids, vulcanizing agents, resins, adhesion aids, antiblocking agents, etc., which can be added in conventional quantities.
According to the invention, the dispersion is preferably prepared without emulsifier addition, but it is optionally possible to use a small quantity of emulsifier. The emulsifier quantity is appropriately below about 3 wt. %, particularly below about 1.5 wt. %. The emulsifier proportion is preferably under 1 wt. %, in particularly preferred manner below 0.5 wt. % or more especially below 0.2 wt. %.
Polymerization is preferably performed between about 50 and 100xc2x0 C., particularly between about 60 and 90xc2x0 C. The temperature can e.g. be dependent on the initiator system used. In certain cases the starting temperature is preferably about 70xc2x0 C. The heat evolution due to the exothermic reaction during polymerization can be used in order to adjust the reaction temperature between 80 and 90xc2x0 C. and optionally it may be necessary to cool so as not to exceed the indicated temperature range. All the amount of heat produced can also be dissipated, so as to maintain the starting temperature of about 70xc2x0 C. throughout the reaction or even to drop below the same. In some cases it is possible to work in an autoclave, which offers the possibility of performing polymerization above 100xc2x0 C. During the radical, aqueous emulsion polymerization, the pH-value of the aqueous dispersing medium is generally 2 to 10. After the end of polymerization, the pH-value can be adjusted to about 2 to 12.
The present invention also relates to a process B) for the preparation of aqueous dispersions of (co)polymerizates using a polymer with cationic functionality, optionally accompanied by the addition of conventional additives, in which the polymer with cationic functionality is obtained by (co)polymerization in an aqueous medium of olefinically unsaturated (co)monomers, in which at least one (co)monomer has a cationic functionality, further (co)monomers are added and polymerization takes place in the presence of suitable initiators, the polymer with cationic functionality being formed in situ in the presence of a seed.
Surprisingly the characteristics of these polymers with cationic functionality are comparable with those of emulsifiers or protective colloids with regards to the (co)polymerizate formed according to the invention, so that the copolymerized particles are stabilized in dispersion. Through a type of xe2x80x9cpolymerizing inxe2x80x9d of the polymer with cationic functionality, a dispersion-stable latex particle is produced, but process B) is directed to a seed polymerization.
In seed polymerization, which is particularly suitable for producing monodisperse latices, a latex with a uniform particle size is initially used. To this seed latex are then dosed in the monomers to be polymerized using a monomer charging procedure. Polymerization is carried out in such a way that the previously introduced latex particles, increase in volume, but do not grow quantitatively, accompanied by the obtaining of monodispersity of the system. The number of particles is proportional to the amount used beforehand and a narrow particle size distribution is obtained. According to the invention, for forming the seed about 0.1 to 25 and in particular about 0.5 to 20 wt. % of the (co)monomer, based on the finished (co)polymerizate are used. The (co)monomers can be the monomers used for the preparation of the cationic polymer or any other monomer (foreign latex). The monomers for preparing the seed are generally independent of the subsequently used monomers.
The (co)polymerizate particles prepared according to the invention by means of the preceding seed polymerization have an extremely homogeneous particle size, i.e. the particles are (substantially) monodisperse. In this context, xe2x80x9cmonodispersexe2x80x9d means that the average particle diameter preferably varies by about xc2x110%. Such homogeneous particle sizes are not always possible with the prior art processes or are frequently associated with high process engineering costs and low yields. In process B) according to the invention, the particle size of the (co)polymerizate produced can be adjusted in planned manner. The latex particles formed preferably have an average diameter of about 30 to 1000 nm, particularly about 50 to 600 nm.
The polymer with cationic functionality can be both a homopolymer, copolymer, block polymer or graft copolymer or also an oligomer and is subject to no other restriction, provided that the cationic polymer has resulted from the (co)polymerization of olefinically unsaturated monomers and has at least one cationic functionality. Reference is made to the examples for process A) with regards to monomers with cationic functionality suitable for preparing the polymer. Preferred monomers with cationic functionality are also quaternary ammonium group-containing monomers. It is obvious to the expert that any (co)polymerizable, olefinically unsaturated starting monomers can be used for this polymer. Preferably, in the polymer with cationic functionality, for about 1 part by weight monomer with cationic functionality there are 0 to about 50 and in particular about 0.1 to 20 parts by weight of (co)monomer.
Thus, according to the invention, the polymer with cationic functionality is prepared by seed polymerization in a preceding stage by homo or (co)polymerization of olefinically unsaturated (co)monomers, in which at least one (co)monomer has a cationic functionality, and is immediately, without being isolated, further processed (further processing in situ). Alternatively the polymer with cationic functionality can be firstly prepared independently of the inventive process, isolated and then further processed. Obviously it is possible to use any commercially available polymer with cationic functionality, which fulfils the aforementioned conditions. Preferably, in the (co)polymerizate obtained, for about 1 part by weight monomer (with cationic functionality) of the polymer with cationic functionality, there are about 2 to 250 and in particular about 10 to 150 parts by weight of other (co)monomers. According to the invention, the (co)polymerizate prepared can contain about 0.001 to 50 mole %, particularly about 0.1 to 35 mole % monomer units with cationic functionality.
With regards to the choice of the (co)monomers, which are polymerized in the presence of the cationic polymer, there are no relevant restrictions to the invention. All (co)polymerizable monomers known to the expert can be used. Reference is made to the comonomers listed for process A) for examples of usable comonomers.
It is preferred that the polymers and/or (co)monomers are selected in such a way that the dispersed (co)polymerizate obtained has a glass transition temperature Tg of more than about 50xc2x0 C. In this connection it is referred to process A).
In a preferred aspect, apart from cationic monomers, it is also possible to copolymerize monomers, whose protonated, reactive group or groups, are deprotonated, accompanied by a corresponding rise in the pH-value. In addition to a cationic functionality, the (co)monomers can have at least one anionic functionality. As a result amphoteric systems can be obtained, which are present in stable form and do not coagulate. Such groups are known to the expert.
As a function of whether the polymer with cationic functionality is prepared separately or in in situ, process B) according to the invention can be performed continuously, semicontinuously or as a batch process and obviously account must be taken of the principles of an emulsion polymerization. In the case of in situ further processing of the cationic polymer, the process can e.g. be performed continuously or as a batch process. The polymerization is carried out in conventional manner between about 50 and 100xc2x0 C., particularly between about 60 and 90xc2x0 C. The temperature can e.g. be dependent on the initiator system used. It is also possible to use here radical initiators, either singly, or as a mixture or optionally with suitable activators, which correspond to those used in illustrating process A). The initiators or initiator combinations are generally used in a quantity of 0.01 to 2 wt. %, based on the total monomers.
As a function of the intended use, the conventional additives known to the expert can be added in suitable quantities. However, the use of emulsifiers is largely obviated, the emulsifier quantity being appropriately below about 3 wt. %, or below about 1.5 wt. %, preferably below 1 wt. %, in particularly preferred manner below 0.5 wt. % or more especially below 0.2 wt. %.
The object of the invention also covers the stabilized, aqueous dispersions obtainable according to the above-described processes A) or B). These are in particular characterized by their high stability and the flexibility of the starting materials.
According to a preferred embodiment of the invention the obtained aqueous dispersion (dispersion 1) of one kind of latex particles can be mixed with a further aqueous dispersion (dispersion 2) with other latex particles. The weight ratio of dispersion 1 to dispersion 2 is preferably in the range of about 5:95 to 95:5, particularly about 10:90 to 90:10, especially about 20:80 to 80:20. Dispersion 2 can comprise an aqueous dispersion of homopolymers or copolymers. Examples of monomers are vinyl acetate, ethylene, vinyl versatate, acrylate, methacrylate, styrene and/or butadiene. Obviously further monomers can also be used which are known by the expert in this technical field. By adding a further dispersion the properties can be optimized accordingly.
The invention also relates to redispersible powders, obtainable from the aforementioned aqueous dispersions after removing the water. Water removal takes place in conventional manner by drying, particularly by spray or freeze drying. Preferably, the redispersible powder according to the invention contains a (co)polymerizate of about 0.01 to 50 wt. % cationic monomers and about 50 to 99.99 wt. % (co)monomers. It is optionally possible to add about 0 to 5 wt. % emulsifiers and conventional additives.
The redispersible powder can be used as a pulverulent finished mixture, which need merely be stirred with water. As a function of the desired application, it can be redispersed in water in more or less concentrated form.
With particular advantage in the present invention, it is possible to achieve a high solids content in the dispersion prepared, a dispersion with up to about 75% solids content in the aqueous medium being possible. Appropriately, generally an aqueous dispersion with about 20 to 60%, particularly about 30 to 50% solids content is prepared.
By mixing a further powder to the obtained powder of the present invention the properties can be optimized accordingly. Thus, powder 1 of one kind of latex particles can be admixed with a further powder 2 of other latex particles. Preferably the weight ratio of powder 1 to powder 2 is in the range of about 5:95 to 95:5, preferably about 10:90 to 90:10, particularly about 20:80 to 80:20. Powder 2 can comprise homopolymers or copolymers which are selected from the following monomers: vinyl acetate, ethylene, vinyl versatate, acrylate, methacrylate, styrene and/or butandiene. This listing is only exemplary and not limiting at all any other monomer can be used herein.